Merge pull request #13980 from wietzesuijker/feat/zarr-build-overviews

Zarr v3: GDALMDArray::BuildOverviews() with >2D support and dataset b…

Author: rouault

autotest/gdrivers/zarr_driver.py

@@ -103,6 +103,16 @@ a ``multiscales`` attribute with a ``layout`` array, the driver exposes
 lower-resolution levels as overviews via :cpp:func:`GDALMDArray::GetOverview`
 and the classic raster band overview API.
 
+Overviews can be generated using :cpp:func:`GDALMDArray::BuildOverviews` or
+equivalently via :cpp:func:`GDALDataset::BuildOverviews` on datasets obtained
+through :cpp:func:`GDALMDArray::AsClassicDataset`. For arrays with more than
+two dimensions, only the spatial dimensions are downsampled; non-spatial
+dimensions (e.g., time) are preserved. Each overview level is resampled
+sequentially from the previous level (e.g., 4x from 2x, not from base).
+Codec settings are inherited from the source array. Calling
+``BuildOverviews`` replaces all existing overviews (unlike the default
+``GDALDataset::BuildOverviews`` behavior which adds new levels).
+
 Kerchunk reference stores
 -------------------------
 

doc/source/drivers/raster/zarr.rst

@@ -579,6 +579,7 @@ Decompressor
 decompressors
 decrementing
 decrypted
+deduplicate
 Deegree
 defacto
 define'ed
@@ -1886,6 +1887,7 @@ multiproc
 multiprocess
 multireadtest
 multirecords
+multiscales
 multispectral
 multistring
 multisurface

doc/source/spelling_wordlist.txt

@@ -673,6 +673,8 @@ class ZarrV3Group final : public ZarrGroupBase
                                          const std::string &osZarrayFilename,
                                          const CPLJSONObject &oRoot) const;
 
+    void GenerateMultiscalesMetadata(const char *pszResampling = nullptr);
+
     std::shared_ptr<GDALMDArray> CreateMDArray(
         const std::string &osName,
         const std::vector<std::shared_ptr<GDALDimension>> &aoDimensions,
@@ -1404,6 +1406,8 @@ class ZarrV3Array final : public ZarrArray
 
     void LoadOverviews() const;
 
+    void ReconstructCreationOptionsFromCodecs();
+
   public:
     ~ZarrV3Array() override;
 
@@ -1436,6 +1440,11 @@ class ZarrV3Array final : public ZarrArray
 
     std::shared_ptr<GDALMDArray> GetOverview(int idx) const override;
 
+    CPLErr BuildOverviews(const char *pszResampling, int nOverviews,
+                          const int *panOverviewList,
+                          GDALProgressFunc pfnProgress, void *pProgressData,
+                          CSLConstList papszOptions) override;
+
   protected:
     std::string GetDataDirectory() const override;
 

frmts/zarr/zarr.h

@@ -3772,11 +3772,15 @@ std::shared_ptr<ZarrGroupBase> ZarrArray::GetParentGroup() const
         if (auto poRootGroup = m_poSharedResource->GetRootGroup())
         {
             const auto nPos = m_osFullName.rfind('/');
-            if (nPos != std::string::npos)
+            if (nPos == 0)
+            {
+                poGroup = std::dynamic_pointer_cast<ZarrGroupBase>(poRootGroup);
+            }
+            else if (nPos != std::string::npos)
             {
                 poGroup = std::dynamic_pointer_cast<ZarrGroupBase>(
-                    poRootGroup->OpenGroupFromFullname(m_osFullName.substr(
-                        0, std::max(static_cast<size_t>(1), nPos))));
+                    poRootGroup->OpenGroupFromFullname(
+                        m_osFullName.substr(0, nPos)));
             }
         }
     }